A semiconductor memory refers to a memory device that is implemented using a semiconductor such as silicon (Si), germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), or the like. A semiconductor memory device is roughly divided into a volatile memory device and a nonvolatile memory device.
A volatile memory device refers to a memory device which loses data stored therein at power-off. The volatile memory device includes a static random access memory (SRAM), a dynamic ram (DRAM), a synchronous DRAM or the like. A nonvolatile memory device refers to a memory device which retains data stored therein even at power-off. The nonvolatile memory device includes a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory device, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), or the like.
In particular, the flash memory device is widely used due to fast operating speed, low power, low noise, large capacity, and the like. The flash memory device stores data using memory elements such as a floating gate memory cell, a charge trap flash memory cell, or the like. Data is stored in the memory elements such as a floating gate memory cell, a charge trap flash memory cell, or the like, by changing their threshold voltages.
A solid state drive (SSD) based on a flash memory can be used as mass storage in a personal computer, a notebook, a workstation, a server system, and the like. Typical SSD devices can be connected with a computing system based on a SATA interface or a PCI-express interface.
However, as the amount of data processed on a computing system increases, needed data throughput may exceed the data bandwidth or communication speed of an interface of the SSD devices, thereby causing a data bottleneck. Since the data bottleneck may cause a decrease in the performance of the computing system, various techniques are being developed to improve the performance.
For example, a double data rate (DDR) interface provides a faster access speed than conventional PCI or SATA interfaces. In addition, a memory module using various kinds of memory devices may be directly connected to a processor.